Automated manual transmission systems that are primarily based on the principle of conventional manual shift transmissions having a countershaft design are generally known from practice, where shifting is performed with the aid of control elements configured as synchronizing elements, which are characterized by the fact that they require little space. In contrast to this, the power-determining elements of a countershaft transmission, which due to their long life and high efficiency are generally configured as spur gears, require a lot of space, which is often limited the case of passenger vehicles.
Transmission concepts having a substantially more compact design are automatic powershift transmissions with planetary gearsets, which may additionally comprise an internal torque split design. While these transmissions, due to their compact design, require relatively little space, it is disadvantageous with this type of transmission that the control elements, such as friction clutches and friction brakes, have to be dimensioned relatively large and be actuated hydraulically. This results in considerable drag losses and an accordingly high level of actuating energy, which influences the efficiency of the transmission negatively.
Furthermore, transmission types are known from practice which attempt to combine the advantages of the countershaft transmissions with respect to their small control elements and the advantages of the automated powershift transmissions comprising planetary gearsets with respect to their compact gearing in that a downstream planetary gearset is provided in a countershaft transmission, thus creating a range-change transmission with purely geometrical ratios. The problem here is, among other things, that the ratios in lower gears are very small, while they are very large in higher gears, making driving the passenger vehicle more difficult.
A combination of features of the above-described transmission types is disclosed in U.S. Pat. No. 5,013,289 with a transmission comprising a countershaft transmission area and two planetary gearsets. Three power paths are provided between a gear input shaft and an output or arranged coaxially thereto, in which the gear ratio can be changed by way of a power shift. By providing three power paths that may be connected to the planetary gearsets, six forward gears can be implemented with relatively few control elements.
The disadvantage here, however, is that the power shift requires the use of multi-disk clutches, resulting in correspondingly high expenses for the design, the hydraulic control and regulation, and that the space requirement of the transmission has not been optimized with respect to the gears that can be shifted with the transmission.
It is, therefore, the object of the present invention to provide a transmission, especially an automated power-split multi-speed transmission, which has been improved compared to the prior art in that it can have a compact design even with a higher number of shiftable gears and can be implemented in a simple layout with little space requirement and which is characterized by good driving behavior.